关于循环

Question

f_jymx
02-20/21
02-20/21
02-20/21
17-09/28
17-09/28
17-09/28
17-09/28
17-09/28
17-09/28
17-09/28
17-09/28
17-09/28
17-09/28
17-09/28
17-09/28
17-09/28
17-09/28
17-09/28
17-09/28
17-09/28
17-09/28
17-09/28
17-09/28
23-24/21
23-24/21
23-24/21
23-24/21
23-24/21
23-24/21
20-02/21
20-02/21
20-02/21
20-02/21
20-02/21
20-02/21
20-02/21
01-15/03
01-15/03
01-15/03
01-15/03
01-15/03
01-15/03
01-15/03
01-15/03
03-01/15
03-01/15
03-01/15
03-01/15
03-01/15
03-01/15
03-01/15
03-01/15
28-17/09
28-17/09
28-17/09
28-17/09
28-17/09
28-17/09
28-17/09
28-17/09
28-17/09
28-17/09
28-17/09
28-17/09
28-17/09
28-17/09
20-02/21
20-02/21
20-02/21
23-24/21
23-24/21
23-24/21
23-24/21
23-24/21
23-24/21
23-24/21
23-24/21
23-24/21
23-24/21
23-24/21
23-24/21
23-24/21
20-02/21
20-02/21
20-02/21
20-02/21
28-17/09
28-17/09
28-17/09
28-17/09
28-17/09
28-17/09
28-17/09
28-17/09
28-17/09
28-17/09
20-02/21
20-02/21
20-02/21
20-02/21
03-01/15
03-01/15
01-15/03
01-15/03
15-03/01
15-03/01
15-03/01
15-03/01
15-03/01
15-03/01
15-03/01
15-03/01
15-03/01
15-03/01
15-03/01
15-03/01
15-03/01
15-03/01
15-03/01
17-24/18
23-21/28
02-20/18
select substring('17-28/03',1,2) as f_jymx from pbjy200708
union
select substring('17-28/03',4,2) as f_jymx from pbjy200708
union
select substring('17-28/03',7,2) as f_jymx from pbjy200708
求子串怎么循环